The present invention relates to an information processor, program, storage medium, and control circuit and, in particular, to an information processor, program, storage medium, and control circuit that provides a power saving function.
In recent years, power saving technology for increasing battery-powered operating time of portable information processing terminals has been receiving attention. For instance, a technology that changes power consumption according to the amount of computation has been used. This is shown, for example, in the “Advanced Configuration and Power Interface Specification Revision 2.0a” (Mar. 31, 2002; Compaq Computer Corporation and four other companies).
A conventional information processing terminal including ACPI capabilities has a normal-operation mode in which coherence control is performed for making data in a processor cache memory identical to data in a main memory and a power-saving mode in which the coherence control is suppressed to lower power consumption from power consumption in normal-operation mode. However, when an input/output device accesses the main memory to perform bus master transfer, the information processing terminal cannot be placed in the power-saving mode because coherence between the cache memory and the main memory would be lost. To solve this problem, an information processor has been proposed that always operates in normal-operation mode. However, such an information processor has the problem of consuming a large amount of power. Another approach has been proposed that flashes a cache memory immediately before the information processor enters power-saving mode. However, this approach has the problem that the cache memory flashing takes long time (for example, a processor requires 80 to 400 microseconds).
It is, therefore, a purpose of the present invention to provide an information processor, program, storage medium, and control circuit that can solve these problems. The purpose is achieved by the combination of features set forth in the independent claims herein. The dependent claims define preferable, specific embodiments of the present invention.